re: the tolerances, (if you look to the right of the above pic at the caps with some silver bands (C7&C10--330pF and 470pF, respectively), at least one must be a tolerance band (i.e. silver = 10%), but there are two of them and I'm not sure which is which.

edit:

IIRC Mouser used to have some of these (tried looking for a datasheet but no luck). Unfortunately, I don't remember the maker, which makes it more difficult to look for a datasheet. Tech 21 Sansamp (the original) also had (one? two?) of those (47nF) I think around the same time as well (early 90s or so).

Sorry, but I insist in my option... those are old design caps so, the first band -yellow in this case- is NOT the first digit value: is just a temperature coefficient... then you have the first and second digit, then you have the multiplier factor and then you have the tolerance.

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Duckman wrote:Sorry, but I insist in my option... those are old design caps so, the first band -yellow in this case- is NOT the first digit value: is just a temperature coefficient... then you have the first and second digit, then you have the multiplier factor and then you have the tolerance.

Yeah, I've seen that method too but look

Example

Brown/black/red/silver/silver. If you take 3 first band as a value and another two for cap spec it will give you 1nF (as per factory schematic). Method described by you in this case isn't relevant

The capacitors used by Marshall in their PCBs up until the late 90's were predecessors to CTC's CA-Series axial ceramic. They were used because they were mounted by insertion machines and were relatively cheap. The dielectric used was Ceramic NPO (Black-band) or Y5P (Silver-band) - light green body. The CA-Series example here is only a 50V DC rated part (this was the only electronic datasheet I could find on the Internet), there was a higher voltage rated part used that was about the size of a 1/4W metal film resistor like the old Philips MFR25; I can't recall that part number or details of.I understand that the last supplier in the UK was Anglia Components Limited in Cambridgeshire - I don''t know if you can still get them.

Attached is an excerpt from the CTC CA-Series Datasheet that will help you decode the colour code used on the body.Panasonic and Taiyo Yuden made similar products and were also used.

If you need to replace these capacitors, replace them with another good quality NPO ceramic (Y5P was used because it was cheaper and readily available), I can suggest AVX. If use an alternate capacitor dielectric, like MKP or MKT, you'll change the sound characteristics of the circuit. Quite some testing and listening went into the prototypes to get the "Marshall Sound" from the circuit.

Regards,

Alex.

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Last edited by alex28m on 19 Jun 2016, 09:34, edited 2 times in total.

Following is the Panasonic datasheet for their leaded axial ceramic capacitors. You'll notice the dielectric varies depending on the capacitance - keep that in mind if you're wanting to keep your repairs true to the original sound of the amplifier's circuit.

The NPO types weren't always available in the larger values and you ended using one of the Y5* dielectric variants that were temperature dependent and became significantly microphonic as the capacitance got larger. Nonetheless, the ac transfer characteristics, and their non-linearity at small signal levels was often something you wanted to give a "characteristic sound" to a circuit.(If you want to know more about capacitor sound, read Cyril Bateman's Capacitor Sound articles that appeared in Wireless World: I saw these have been published here:https://linearaudio.nl/cyril-batemans-capacitor-sound-articles

A lot of the film capacitor types give a "clean" sound or in the words of my old boss, "...those capacitors sound too bloody Hi-Fi and were not making any of that..." - the ceramics were used for good reason in most cases

Alex.

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